Question

Beer's Law states that $A=abc$, where A is absorbance, a is the molar absorptivity constant, b is the path length, and c is the molar concentration.
Which of the following would be an incorrect application of Beer's Law?

• A. The path length is irrelevant, as long as it is inversely proportional to the molar concentration when determining the concentration of an unknown as compared to a standard curve.
• B. The molar concentration is directly related to absorption of light by the sample and is used to develop a standard curve.
• C. The concentration of an unknown sample can be easily determined from a standard curve of known concentrations plotted against absorbance for a fixed path length.
• D. The use of Beer's Law and a spectrophotometer for a colored sample is a better method of determining molar concentration than visual comparison.

Answer 1

The correct option is A The path length is irrelevant, as long as it is inversely proportional to the molar concentration when determining the concentration of an unknown as compared to a standard curve.

The standard curve is the graph of obserbance versus concentration. The path length is relevant, because it is known, we can easily find the molar absorptinity constant with the help of slope of the graph and Beer's law.